This project is designed to study the mechanism of the increased microvascular permeability to macromolecules produced by various naturally occuring vasoactive agents, and the interaction of these edemogenic substances with the sympathoadrenal system, naturally occurring, and synthetic vasoactive agents which possess the unique ability to either antagonize or potentiate the increase in macromolecular permeability produced by the endemogenic agents by a direct action on the microvascular membrane. Pharmacological, physiological, and anatomical techniques will be employed to link the site of macromolecular leakage to vessel wall anatomy, and to determine the mechanism(s) of the increases in macromolecular permeability.